Search PubMed⌕ Search

Biomedical subjects

D A Wright

Publications and source records attributed to D A Wright.

At least 91 records · Page 5Linked to original sources
PubMed1983

Two sex-linked loci in the leopard frog, Rana pipiens.

Crosses involving one heterozygous parent were performed to test the inheritance of enzymes in the leopard frog, Rana pipiens. After metamorphosis, offspring were sexed and tissue extracts from them were analyzed by gel electrophoresis. Enzyme genotype and sex showed independent assortment for 10 of 12 enzymes heterozygous in the male parent. However, among the offspring of males heterozygous for peptidase C (Pep-C) or superoxide dismutase 1 (SOD-1), male progeny tend to inherit one allele, whereas female progeny tend to inherit the other. Data from several different crosses yield recombination frequencies of 8.6% between sex and SOD-1, 6.9% between SOD-1 and Pep-C and 12.1% between sex and Pep-C. When the female parent is heterozygous for these enzymes no significant difference is seen, in the offspring, between male and female homozygotes and heterozygotes. These results confirm that males are the heterogametic sex in R. pipiens and suggest that sex is determined by a small number of genes on otherwise identical X and Y chromosomes.

Animals↗
PubMed1982

Regulation of glyceraldehyde-3-phosphate dehydrogenase: inheritance and biochemistry of a low-activity genetic variant in the platyfish, Xiphophorus maculatus.

Analysis of an electrophoretic variant coded by the glyceraldehyde-3-phosphate dehydrogenase-2 (GAPD2) locus of the platyfish (Xiphophorus maculatus) revealed that the variant allele produced a defective subunit. As a homotetramer (from tissue extracts of homozygotes), the variant enzyme had only 12% the activity of homotetramers specified by the normal allele. In heterozygotes the defective subunits aggregated with the normal subunits to produce hybrid tetramers in the amounts expected for equal production of the two subunits by the two alleles but with the activity reduction expected according to the subunit composition. The total activities of muscle extracts in heterozygotes were reduced to about 55% of normal, consistent with that expected if neither compensatory synthesis of allelic products of the GAPD2 locus nor the GAPD1 locus took place. This result implies that regulation of the production of this enzyme is constitutive (produced at maximal rate) or depends on a mechanism which does not recognize the functional activity of the gene products. The absence of detectable segregation distortion suggests that the variant had no significant effect on viability, and thus may be selectively neutral, though producing in several tissues an activity deficiency of 88% in homozygotes.

Alleles↗
PubMed1982

Chromosome-bound mitotic factors: release by endonucleases.

Additional evidence is presented to support our recently reported conclusion that the mitotic factors of mammalian cells, which induce germinal vesicle breakdown and chromosome condensation when injected into fully grown Xenopus laevis oocytes, are localized on metaphase chromosomes. Chromosomes isolated from mitotic HeLa cells were further purified on sucrose gradients and digested for varying periods with either the micrococcal nuclease or DNase II. At each time point of digestion the amount of mitotic factors released was determined by injecting a supernatant of these fractions, obtained by high-speed centrifugation, into oocytes. The amount of DNA rendered acid soluble under the conditions of digestion used was 3% ot 5% of the total chromosomal DNA. The extent of release of mitotic factors with both nucleases was estimated to be about 30% to 40% as evidenced by the reextraction of the undigested chromosomal pellet with 0.2 M NaC1. Similar results were obtained when nuclei from G2 cells were digested under identical conditions. The release of these chromosome-bound mitotic factors by mild digestion with these nucleases though only partial, clearly demonstrates that a significant proportion of these factors are localized on metaphase chromosomes.

Animals↗
PubMed1982

Peptidase isozymes of the leopard frog Rana pipiens: properties and genetics.

The substrate specificity of five peptidases in tissues of the leopard frog, Rana pipiens, corresponds to mammalian peptidases (Pep) A, B, C, D, and S. The inheritance of electrophoretic variants of Pep A, B, C, and D verifies the genetic basis of the variants and the control of the enzymes by separate genetic loci. Electrophoretic patterns of heterozygotes suggest that Pep A, B, and D are dimers, whereas Pep C has a monomer structure. The tissue distribution and developmental patterns suggest that frog peptidases are subject to cellular regulation. Tests of genetic linkage show independent assortment for Pep A and Pep C and for Pep C and Pep D. Pep C is closely linked to superoxide dismutase-1 (6.87% recombination), and Pep B is linked to mannose phosphate isomerase (30.4% recombination).

Aminopeptidases↗
PubMed1982

Effect of nuclear magnetic resonance on early stages of amphibian development.

Frog spermatozoa, fertilized eggs (during second meiotic division), and embryos (during cleavage) were subjected separately to 30 MHz continuous wave NMR exposure in a static magnetic field of 7.05 kG for 20 min and were compared to unexposed groups, at similar stages, with respect to damage in genetic material, interference with meiotic cell division, and impairment in the development of embryos. No significant differences were observed following treatment suggesting that NMR exposure, at the dose used, does not cause detectable adverse effects in this amphibian.

Animals↗
PubMed1982

Localization of mitotic factors on metaphase chromosomes.

The objective of this study was to determine whether the mitotic factors of HeLa cells, which induce meiotic maturation, i.e. germinal vesicle breakdown (GVBD) and chromosome condensation, when injected into fully grown Xenopus laevis oocytes, were localized in the cytoplasm or associated with the metaphase chromosomes. Cytoplasmic extracts were prepared by lysing mitotic HeLa cells in low-salt hypotonic buffer and separating the chromosomes by centrifugation. Th mitotic factors bound to chromosomes were extracted with high-salt (0.2 M-NaCl) buffer. Both the cytoplasmic and chromosomal protein fractions were evaluated for their maturation-promoting activity (MPA) in the Xenopus oocytes. The results of this study indicate that both the cytoplasmic and chromosomal fractions are identical in many respects, including their ability to induce GVBD, but the specific activity of the chromosomal fraction was at least threefold greater than that of the cytoplasmic fraction. These data suggest that a major portion of the mitotic factors is localized on the metaphase chromosomes. This association does not appear to be due to adventitious binding of mitotic proteins to chromosomes during the extraction procedures. Furthermore, when extracts were prepared in a similar way from early- and mid-G2-phase HeLa cells, only the nuclear extracts had MPA and no activity was found in the cytoplasmic fraction. Both the cytoplasmic and nuclear extracts of late-G2 cells exhibited MPA. These data support the conclusion that the mitotic factors become preferentially bound to chromatin as soon as they are synthesized, and as the cell synthesizes more of these factors in preparation for mitosis, increasing amounts of them are retained in the cytoplasm.

Animals↗
PubMed1981

The regeneration of segment boundaries.

The segment borders in the abdomen of Oncopeltus (Hemiptera) are both elements in the integumental pattern and compartment boundaries. When regions of the cuticle and epidermis are extirpated, and the free edges joined together, intercalation occurs. This intercalation always takes the shortest available route along the 'segmental wavelength', and can result in the formation of an adventitious segment boundary.

Animals↗
PubMed1981

The effect of calcium on cadmium toxicity in the freshwater amphipod, Gammarus pulex (L.).

Adult intermolt Gammarus pulex were exposed to a range of cadmium concentrations in an artificial stream water containing 20 mg calcium 1(-1). 96 hr and 48 hr LC-50 values obtained were 0.12 and 0.68 mg Cd 1(-1), respectively. The influence of external calcium level on cadmium toxicity was investigated at a cadmium concentration of 0.5 mg 1(-1). Calcium had an antagonistic effect on cadmium toxicity, and at a calcium concentration of 200 mg 1(-1) experimental animals failed to reach 50% mortality after a period of 120 hr. Over a 48 hr period of Cd uptake a solution containing 5 mg Cd 1(-1), animals in 200 mg calcium 1(-1) accumulated only half as much cadmium as animals in 20 mg calcium 1(-1). Post-molt animals were very much more sensitive to cadmium than intermolt specimens. Exposure to 0.1 mg Cd 1(-1) resulted in death in approximately 24 hr and the mean mortality time for animals in 0.01 mg Cd 1(-1) was 45 hr. These data are likely to be explained in terms of competition between cadmium and calcium for binding sites associated with key physiological processes. The results place these animals among the most sensitive organisms yet studied with regard to cadmium toxicity, and emphasize the importance of the molt in assessing toxic effects on crustaceans.

Animals↗
PubMed1981

Chromosome condensing ability of mitotic proteins diminished by the substitution of phenylalanine with parafluorophenylalanine.

One of the objectives of this study was to develop a method for the reversible arrest of HeLa cells in G2 phase by using p-fluorophenylalanine (FPA), an analog of phenylalanine. Addition of 0.5 mM of FPA to synchronized HeLa cells during the middle of S phase, i.e., 4 h after reversal of the double thymidine block, arrested 93% of the cells in G2 phase. After the drug was removed from the medium, these G2 cells proceeded into mitosis synchronously. The results of the study also indicate that incorporation of FPA into mitotic proteins results in the inhibition of chromosome condensation as assayed by their ability to induce premature chromosome condensation in G1 HeLa cells and meiotic maturation in amphibian oocytes.

Animals↗
PubMed1980

Inheritance of enzymes and blood proteins in the leopard frog, Rana pipiens: three linkage groups established.

Individuals from natural populations of the leopard frog, Rana pipiens, were analyzed for electrophoretic differences in blood proteins and enzymes from an amputated digit. The proteins examined represent products of 72 loci. Presumptive heterozygotes at multiple loci were selected for experimental crosses. Mendelian inheritance of 18 protein variations were demonstrated in the offspring. Tests for linkage or independent assortment were performed for 75 locus pairs. Three linkage groups were established. Linkage group 1 contains two loci, aconitase-1 (Acon 1) and serum albumin (Alb), with a 19% recombination frequency between them. Linkage group 2 contains four loci, glyoxalase (Gly), acid phosphatase-1 (Ap1), acid phosphatase-2 (AP2), and esterase-5 (Est5). The data show the relationships Gly-21.1%-AP1-0%-AP2-6.3%-Est5, and Gly-25.6%-Est5. Linkage group 3 consists of four closely linked esterase loci. The data, Est1-5.1%-Est6, Est6-1.8%-Est10-1.9%-Est4 and Est6-3.0%-Est4, do not establish a complete order but suggest that Est10 is between Est4 and Est6. These results, with data demonstrating apparent independent assortment of 67 other locus pairs, provide a foundation for establishing the frog genetic map.

Animals↗
PubMed1979

Mitotic factors from mammalian cells: a preliminary characterization.

The objective of this study was the preliminary characterization of the factors from mitotic HeLa cells that can induce meiotic maturation in Xenopus laevis oocytes. We found that this factor is a heat-labile, Ca2+-sensitive, nondialyzable protein with a sedimentation value of 4-5S. Furthermore, no new protein synthesis was found to be required for this mitotic factor to induce maturation in the amphibian oocytes. These data suggest that the factors involved in the breakdown of nuclear membrane and the condensation of chromosomes that are associated with three different phenomena, mitosis, meiosis, and premature chromosome condensation, are very similar in different animal species.

Animals↗
PubMed1979

Mitotic factors from mammalian cells induce germinal vesicle breakdown and chromosome condensation in amphibian oocytes.

Cytoplasmic extracts of HeLa cells synchronized in various phases of the cell cycle were injected into fully grown Xenopus laevis oocytes to monitor the presence of factors that can induce meiotic maturation: i.e., germinal vesicle breakdown and chromosome condensation. Extracts from GI and S phase cells had no activity. The maturation-inducing activity, which was found to be low during early and mid G2 phases, increased rapidly during late G2 and reached a peak in mitosis. The results of this study suggest that the factors that regulate the breakdown of nuclear membrane and chromosome condensation during mitosis, meiosis, and premature chromosome condensation appear to be very similar, if not identical, throughout the animal kingdom.

Animals↗